Layer-by-Layer Fabrication of Core–Shell Fe₃O₄@UiO-66-NH₂ with High Catalytic Reactivity toward the Hydrolysis of Chemical Warfare Agent Simulants

Detoxifying materials against chemical warfare agents (CWAs) and their simulants are highly desired for proper handling of contamination by and destruction of CWAs. Herein, we report a facile layer-by-layer fabrication of core–shell Fe3O4@UiO-66-NH2 and its application in fast degradation of CWA simulants. The Fe3O4@UiO-66-NH2 composite was prepared through a layer-by-layer epitaxial growth strategy, by alternately immersing Fe3O4 nanoparticles in ethanol solutions of a metal node [Zr6O4(OH)4]12+ precursor and organic linkers [NH2-BDC, 2-aminoterephthalic acid], respectively, and separating using a magnet. As confirmed by characterization results, the Fe3O4@UiO-66-NH2 composites with 24.4 μmol/g Zr6 node content showed a well-defined core–shell structure as well as good thermal and chemical stability. These core–shell magnetic metal–organic frameworks (MOFs) were further tested in the catalytic hydrolysis of dimethyl-4-nitrophenyl phosphate (a nerve agent simulant) and demonstrated 36 times higher catalytic activity than the UiO-66-NH2 powder due to their highly defective surface, high percentage of MOFs on the surface, and their rich mesoporous structure. Since magnetism was retained after the coating of MOFs, Fe3O4@UiO-66-NH2 could be easily recovered and reused after catalysis.